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Date November 2018 Marks available 2 Reference code 18N.3.sl.TZ0.7
Level SL Paper 3 Time zone TZ0
Command term Deduce Question number 7 Adapted from N/A

Question

Lipids play several roles in our bodies.

A phospholipid generally consists of two hydrophobic fatty acids and a hydrophilic group.

Fatty acids are products of the acidic hydrolysis of phospholipids. Deduce the names of the other two products.

[2]
a.

The iodine number is the maximum mass of iodine that reacts with 100 g of an unsaturated compound.

Determine the iodine number of stearidonic acid, C17H27COOH.

[3]
b.i.

State two functions of lipids in the body.

[2]
b.ii.

Outline one effect of increased levels of low-density lipoproteins in the blood.

[1]
c.

Markscheme

phosphoric acid ✔

glycerol/propane-1,2,3-triol ✔

 

Do not accept formulas.

a.

ALTERNATIVE 1:

4 C=C bonds/4 carbon to carbon double bonds ✔

mass of iodine per mole of acid = «4 × 253.80 g mol–1 =» 1015.2 «g mol–1» ✔

iodine number «= 1015.2 g mo l 1 276.46 g mo l 1 × 100 » = 367 ✔

 

ALTERNATIVE 2:

4 C=C bonds/4 carbon to carbon double bonds ✔

« 100 g 276.46 g mo l 1 × 4 =» 1.447 mol of I2 «reacts with 100 g» ✔

iodine number «= 1.447 mol × 253.80 g mol–1» = 367 ✔

Award [3] for correct final answer.

b.i.

Any two of:

«structural» components of cell membranes ✔

energy storage/utilization ✔

«thermal/electrical» insulation ✔

transport «of lipid-soluble molecules» ✔

hormones/chemical messengers ✔

 

Accept other specific functions, such as “prostaglandin/cytokine/bile acid synthesis”, “cell differentiation/growth”, “myelination”, “storage of vitamins/biomolecules”, “signal transmission”, “protection/padding of organs”, “precursors/starting materials for the biosynthesis of other lipid”.

b.ii.

Any one of:

atherosclerosis/cholesterol deposition «in artery walls» ✔

heart/cardiovascular disease ✔

stroke ✔

 

Accept “arteries become blocked/walls become thicker”.

c.

Examiners report

[N/A]
a.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
c.

Syllabus sections

Options » B: Biochemistry » B.3 Lipids
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